ME6412 THERMAL ENGINEERING LABORATORY I 2015

D1 PREPARED BY BIBIN.C and S.GOBINATH, AP/MECH, RMKCET

4. ACTUAL INDICATOR DIAGRAM FOR A FOUR STROKE CYCLE PETROL ENGINE

Exp. No. : Date:

Aim :

To study the actual indicator diagram for a four stroke cycle petrol engine.

Actual indicator diagram for a four stroke cycle petrol engine:

The actual indicator diagram for a four stroke cycle petrol engine is shown. The

suction stroke is shown by the line 1-2, which lies below the atmospheric pressure line. It

is this pressure difference, which makes the fuel-air mixture to flow into the engine

cylinder. The inlet valve offers some resistance to the incoming charge. That is why, the

charge cannot enter suddenly into the engine cylinder. As a result of this, pressure inside

the cylinder remains somewhat below the atmospheric pressure during the suction stroke.

The compression stroke is shown by the line 2-3, which shows that the inlet valve closes

(lVC) a little beyond 2 (i.e. BDC). At the end of this stroke, there is an increase in the

pressure inside the engine cylinder. Shortly before the end of compression stroke (i.e.

TDC), the charge is ignited (lGN) with the help of spark plug as shown in the figure. The

sparking suddenly increases pressure and temperature of the products of combustion. But

the volume, practically, remains constant as shown by the line 3-4. The expansion stroke

is shown by the line 4-5, in which the exit valve opens (EVO) a little before 5 (i.e. BDC).

Now the burnt gases are exhausted into the atmosphere through the exit valve. The

exhaust stroke is shown by the line 5-1, which lies above the atmospheric pressure line. It

ME6412 THERMAL ENGINEERING LABORATORY I 2015

D2 PREPARED BY BIBIN.C and S.GOBINATH, AP/MECH, RMKCET

is this pressure difference, which makes the burnt gases to flow out of the engine

cylinder. The exit valve offers some resistance to the outgoing burnt gases. That is why

the burnt gases cannot escape suddenly from the engine cylinder. As a result of this,

pressure inside the cylinder remains somewhat above the atmospheric pressure line

during the exhaust stroke

Result:

Thus the actual indicator diagram for a four stroke cycle petrol engine was

studied.